cDNA from hepatitis A virus (HAV) has been cloned into pBR 322. Six cDNA clones which together span the entire genome of HAV have been isolated. These clones have been ligated together to form a single clone which was thought to represent a cDNA analog of full-length HAV in pBR 322. In addition, the HAV cDNA was inserted into an SV40 vector. Transfection of both tissue culture cells (in vitro) and marmosets (in vivo) with these plasmids failed to generate HAV. Fine structure mapping of the HAV cDNA subsequently indicated that about 40 base pairs had been deleted during the ligation process. Construction of a full-length infectious HAV cDNA clone is in progress.